There's Maria obviously, but big sis will never allow that. Hikaru-chan his first love and first kiss! He doesn't seem to be going anywhere anyway any time soon, so probably more teasing. Rui never liked him, but it seems he doesn't care anymore(or doesn't have time to) after it was revealed lil senpai scored her big sister the gravure idol, so this one seems out. Lately it seems Maho is interested, though senpai is too oblivious to notice, also she can't overstep Maria, so I don't think it will go anywhere any time soon.
In any case since it's a comedy 4-koma don't expect anything to ever go for him anywhere in the romance department.